The present invention relates to an aluminum surface treatment process and an aluminum composite material having an aluminum nitride surface region formed by the aluminum surface treatment process.
Aluminum nitride (AlN) is known for its good thermal conduction and electrical insulation capabilities and high durability such as resistance to heat, corrosion, wear, impact, crack etc. and compressive stress relaxation ability. Various treatment processes have been thus proposed to produce aluminum composite materials with aluminum nitride surface regions (layers) for improvements in material surface properties.
Japanese Laid-Open Patent Publication No. 60-211061 (abbreviated as “JP60-211061A”) discloses an aluminum composite production process that includes the steps of activating a surface of an aluminum material and ion nitriding the activated surface of the aluminum material by glow discharge so as to form a coating layer of aluminum nitride on the aluminum material. In JP60-211061A, however, the aluminum nitride layer has a thickness of the order of several micrometers, at most, over ten micrometers and cannot be controlled to a sufficient thickness. It takes long time e.g. more than 24 hours to form the aluminum nitride layer even with such a small thickness during the ion nitriding. The aluminum nitride layer also lacks in homogeneity. The resulting aluminum composite material thus fails to attain sufficient durability and increases in process cost. Further, the aluminum nitride layer does not show good adhesion to the aluminum material so that it is likely that the aluminum nitride layer will become separated from the aluminum material.
Japanese Laid-Open Patent Publication No. 5-179420 (abbreviated as “JP5-179420A”) discloses an aluminum composite production process that includes the steps of forming an intermediate layer of Al—Ag metal compound on an aluminum material and forming an aluminum nitride layer on the intermediate metal compound layer. In JP5-179420A, the aluminum nitride layer increases in thickness, homogeneity, durability and adhesion to the aluminum material. It is however likely that the aluminum nitride layer will become cracked when the thickness of the aluminum nitride layer exceeds 10 μm. In addition, the use of Ag in the intermediate metal compound layer and the preparation of the intermediate metal compound layer in thin-film form are essential to the aluminum composite production process. The resulting aluminum composite material thus increases in material and process cost. Moreover, the flexibility of mechanical strength of the aluminum composite material becomes poor as the strength of adhesion between the aluminum material and the aluminum nitride layer depends on the intermediate metal compound layer.
International Patent Publication No. WO2004/065653 discloses an aluminum composite production process that includes the steps of preparing a CuAl2-containing aluminum material and plasma nitriding the aluminum material so as to form an aluminum nitride layer on the aluminum material. In WO2004/065653, the aluminum nitride layer can be formed with a relatively large thickness and some degree of homogeneity, durability and adhesion to the aluminum material.